Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 247

The most common type of furnace in the electric utility industry is the dry, bottom- pulverized feedstock boiler. When pulverized feedstock is burned in a dry, bottom boiler, approximately 80% w/w of the unburned material or ash is entrained in the flue gas and is captured and recovered as fly ash. The remaining 20% w/w of the ash is dry bottom ash, a dark gray, granular, porous solid that is collected in a water-filled hopper at the bottom of the furnace. When a sufficient amount of bottom ash drops into the hopper, it is removed by means of high-pressure water jets and conveyed by sluiceways, either to a disposal pond or to a decant basin for dewatering, crushing, and stockpiling for disposal or use.

Bottom ash is the coarser component of the ash and may comprise a substantial portion of the waste. Rather than floating into the exhaust stacks, it settles to the bottom of the power plant boiler. Bottom ash is not quite as useful as fly ash, although power plant owners have tried to develop options for beneficial use options, such as structural fill and road-base material. However, the bottom ash remains toxic when recycled and can leak heavy metals into the groundwater.

See also: Ash, Biomass Ash, Boiler Slag, Fly Ash.